Most of the flowers in nature are red, orange and yellow. If we have seen a black flower, it’s chance in a million.

People have made a survey to colors of more than four thousand kinds of flowers and discovered that only eight of them are black.

As we know, sunlight is formed by seven colored lights. The wavelength of each light is also different, so the quantity (量) of heat in each light is also different. Flowers, especially their petals (花瓣)，are easy to be harmed by high temperature.

Black flowers can take in the light of all the wavelengths that make them dry up because of high temperature, so black flowers can hardly resist (抵抗) sunlight. But red, orange and yellow flowers can protect themselves from sunlight by reflecting (反射) the red light, orange light and yellow light, each of which has a large quantity of heat.

Most of us use the alarm clock to wake up at the right time for school or work. We look at our watches to know the right time for the bus or train. However, there is also a right time to eat, sleep, exercise and take medicine. We can’t look at a clock for the right time for these activities. We must listen to the biological clock inside everyone’s body, which is a natural system in living things that controls regular physical activities such as sleeping.

Barbara exercised every morning. She woke up at 6: 00 a. m. She ran about two miles before she went to work. But Barbara’s legs and back started to hurt. She did some exercise before she ran. But her legs and back still hurt. She ran more slowly, but the pain didn’t stop. Barbara talked to her doctor. The doctor said, “Don’t run in the morning. Try to exercise later in the day because that is the time when your body is at the right temperature for exercise after work.” She followed the doctor’s advice and her legs and back didn’t hurt anymore.

Today, doctors are learning more about “chronobiology”, which means the study of biological clocks. They are learning about the importance of time for our bodies. For example, it is best for people to go to sleep on time every night and to eat only when they’re hungry. Also, doctors discovered that some illnesses, such as heart attacks, happen most often in the morning. This information tells them that the best time for the person with a heart attack to take heart medication may be at night. When patients take heart medication at night, they may prevent a heart attack in the morning.

Because of the great importance of the biological clock, many doctors believe chronobiology can help us live healthier lives. Maybe it’s time for us to listen to the clock inside our bodies.

Adolescence (青春期) is the time between being a child and full adult (成人). Adolescence is a difficult process (过程) for teenagers. The reason is that both their minds and bodies make great changes. The changes may cause many problems if teenagers don’t know what to do with them. So it’s necessary to learn something about the changes.

Different people begin adolescence at different ages. Usually girls start adolescence two years earlier than boys. For both girls and boys, adolescence is usually over by the age of 18.

Teenage boys at this time often begin to take unnecessary risks. They want others to accept them. They are also easily angry with others and fight more. So, they need to think before they act and make good decisions for themselves.

A girl’s personality often does not develop in the same way as a boy’s. Teenage girls sometimes lose confidence (信心) in themselves. They aren’t sure about their own feelings, but they are usually afraid to tell others about their problems.

We can do a lot to care for and help teenagers. At the same time, parents can also tell teenagers about what is happening to them and help them to know themselves better. Everyone plays a part in making sure that young people grow into healthy adults.